A coroner has again pleaded for families not to sleep with infants after a Lower Hutt baby died of sudden unexpected death in infancy (SUDI) - cot death.

The baby's mother found he had turned blue when she woke and he reached for his mother's face before dying in her arms, the coroner said.

Astyn Ioata was only 5-1/2 months old when he died in the single bed he was sharing with his mother on March 31, 2012.

In a finding released today, Coroner Ian Smith pleaded with parents not to sleep with their babies and educate themselves about the risk of SUDI.

"I must again echo the continuing plea, by coroners, for families to eliminate unsafe sleeping environments with babies," he said.

The baby's mother said she been sleeping with the baby because she had mistakenly associated cot-death with leaving her baby in a cot.

"She had little understanding of SUDI prevention strategies ... especially choosing to co-sleep, as the mother was worried about 'cot death' if the baby slept in a cot," he said.

However the coroner noted that a report from the Plunket nurse who had visited the family stated that on each of the visits SUDI prevention had been discussed with the mother.

The coroner's report said that at 9.30pm the night before his death, Astyn was put down by his mother in the bed they shared.

He woke once at 4am to feed and went back to sleep.

When his mother woke at 8am, she found her baby face down and blue. As she picked him up he made an apparent effort to reach for her face before closing his eyes and dying, the coroner said.

Footnote: About 70 babies die unexpectedly in their sleep in New Zealand every year. Most of these deaths can be prevented by ensuring they are breastfed, are in smoke-free environments and are sleeping safely.